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Tue, 22 Sep 2026 09:39:44 -0700 (PDT) Message-ID: <41f8ed8e-1466-4002-8411-bf9871da2adc@gmail.com> Date: Tue, 22 Sep 2026 19:39:41 +0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] HID: multitouch: add support for Goodix GXTP7863 touchpad To: Benjamin Tissoires Cc: jikos@kernel.org, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260814171247.16707-1-daminovruzal7@gmail.com> <20260819123326.3242-1-daminovruzal7@gmail.com> <51055e02-5bf1-4b1e-b430-382d00d3d004@gmail.com> <33a7c239-ede5-4091-ba72-ff429d97013c@gmail.com> <816a300c-1f63-4d4a-a0f9-8eef5bd7e748@gmail.com> Content-Language: en-US From: Ruzal In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/22/26 4:24 PM, Benjamin Tissoires wrote: > Actually, after a lot of debugging, it turns out that the session stall > was a red herring: it's hid-replay's behavior which basically only > listen for SET_REPORT events before it is ready, but then ignores > everything else. > > And in the case where the UNKNOWN input node didn't have the KEY_*, > systemd-logind would not keep the hid node opened, and would further > re-open it, 3 times, and 3 times we have a timeout of 5 seconds due to > uhid not responding to SET_REPORT. > > TL;DR: changing the report descriptor is doable, and there won't be this > session lock with a real device. > > Regarding the `map_abs(ABS_MISC)`, you are almost correct. The solution > is simply to not use an unknown vendor usage. the second vendor > collection is 0xff00, which matches HID_UP_MSVENDOR which goes to > ignore. > > So making the 0xff01 bogus collection 0xff09 (HID_UP_LOGIVENDOR2) or any > other HID_UP_LOGIVENDOR* also goes to ignore, and the phantom node just > disappears. > > And TL;DR of rest, changing the usage page of the report ID 8 from > 0xff01 to 0xff09 solves the problem entirely :) > > > Thanks for this attempt, however, this is not great because there are > multiple checks for MT_CLS_WIN_8 throughout the code, and so your patch > misses them. > > It is not great to have a BPF to work around a kernel bug, but in that > case I think that's the most sensible thing to do. A proper fix is to > restrict the parsing of 0xff01 for non keyboards or for non HP machines, > but as mentioned previously, this is prone to regressions :( > > Also, I've just checked the fwupd sources, and I think changing the > vendor collection is fine. Hopefully this won't break any user space > program, but OTOH the touchpad is pretty unusable at the moment. > > Cheers, > Benjamin Hi Benjamin, Got it, the uhid SET_REPORT explanation makes a lot of sense. Are you already working on the BPF fixup, or should I write it and open a merge request in the udev-hid-bpf repo? I can test it anytime. Cheers, Ruzal